From 2e3a1e767d35b9008cdaa11a87ce6485c0487050 Mon Sep 17 00:00:00 2001
From: Ethan Atkins <contact@ethanatkins.com>
Date: Tue, 17 Dec 2019 12:46:14 -0800
Subject: [PATCH] Don't poll System.in in ConsoleChannel

The ask user thread is a background thread so it's fine for it to block
on System.in. By blocking rather than polling, the cpu utilization of
sbt drops to 0 on idle. We have to explicitly handle <ctrl+d> if we
block though because the JLine console reader will return null both if
the input stream returns -1
---
 .../scala/sbt/internal/util/LineReader.scala  |  2 ++
 .../scala/sbt/internal/util/Terminal.scala    | 13 ++++++++++
 .../scala/sbt/internal/ConsoleChannel.scala   | 24 ++++++++++++-------
 3 files changed, 31 insertions(+), 8 deletions(-)

diff --git a/internal/util-complete/src/main/scala/sbt/internal/util/LineReader.scala b/internal/util-complete/src/main/scala/sbt/internal/util/LineReader.scala
index b8704c97c..660406559 100644
--- a/internal/util-complete/src/main/scala/sbt/internal/util/LineReader.scala
+++ b/internal/util-complete/src/main/scala/sbt/internal/util/LineReader.scala
@@ -94,6 +94,7 @@ private[sbt] object JLine {
   @deprecated("Handled by Terminal.fixTerminalProperty", "1.4.0")
   private[sbt] def fixTerminalProperty(): Unit = ()
 
+  @deprecated("For binary compatibility only", "1.4.0")
   private[sbt] def makeInputStream(injectThreadSleep: Boolean): InputStream =
     if (injectThreadSleep) new InputStreamWrapper(originalIn, 2.milliseconds)
     else originalIn
@@ -176,6 +177,7 @@ final class FullReader(
     val handleCONT: Boolean,
     inputStream: InputStream,
 ) extends JLine {
+  @deprecated("Use the constructor with no injectThreadSleep parameter", "1.4.0")
   def this(
       historyPath: Option[File],
       complete: Parser[_],
diff --git a/internal/util-logging/src/main/scala/sbt/internal/util/Terminal.scala b/internal/util-logging/src/main/scala/sbt/internal/util/Terminal.scala
index 5322b5869..44a15caf4 100644
--- a/internal/util-logging/src/main/scala/sbt/internal/util/Terminal.scala
+++ b/internal/util-logging/src/main/scala/sbt/internal/util/Terminal.scala
@@ -8,6 +8,7 @@
 package sbt.internal.util
 
 import java.io.{ InputStream, OutputStream }
+import java.nio.channels.ClosedChannelException
 import java.util.Locale
 import java.util.concurrent.atomic.{ AtomicBoolean, AtomicReference }
 import java.util.concurrent.locks.ReentrantLock
@@ -54,6 +55,18 @@ object Terminal {
    */
   def systemInIsAttached: Boolean = attached.get
 
+  /**
+   * Returns an InputStream that will throw a [[ClosedChannelException]] if read returns -1.
+   * @return the wrapped InputStream.
+   */
+  private[sbt] def throwOnClosedSystemIn: InputStream = new InputStream {
+    override def available(): Int = WrappedSystemIn.available()
+    override def read(): Int = WrappedSystemIn.read() match {
+      case -1 => throw new ClosedChannelException
+      case r  => r
+    }
+  }
+
   /**
    * Provides a wrapper around System.in. The wrapped stream in will check if the terminal is attached
    * in available and read. If a read returns -1, it will mark System.in as unattached so that
diff --git a/main-command/src/main/scala/sbt/internal/ConsoleChannel.scala b/main-command/src/main/scala/sbt/internal/ConsoleChannel.scala
index 12c4bfcce..f18fa2981 100644
--- a/main-command/src/main/scala/sbt/internal/ConsoleChannel.scala
+++ b/main-command/src/main/scala/sbt/internal/ConsoleChannel.scala
@@ -8,12 +8,14 @@
 package sbt
 package internal
 
-import sbt.internal.util._
-import BasicKeys._
 import java.io.File
+import java.nio.channels.ClosedChannelException
+
+import sbt.BasicKeys._
+import sbt.internal.util.Util.AnyOps
+import sbt.internal.util._
 import sbt.protocol.EventMessage
 import sjsonnew.JsonFormat
-import Util.AnyOps
 
 private[sbt] final class ConsoleChannel(val name: String) extends CommandChannel {
   private var askUserThread: Option[Thread] = None
@@ -23,13 +25,19 @@ private[sbt] final class ConsoleChannel(val name: String) extends CommandChannel
       case Some(pf) => pf(s)
       case None     => "> "
     }
-    val reader = new FullReader(history, s.combinedParser, JLine.HandleCONT, true)
+    val reader =
+      new FullReader(history, s.combinedParser, JLine.HandleCONT, Terminal.throwOnClosedSystemIn)
     override def run(): Unit = {
       // This internally handles thread interruption and returns Some("")
-      val line = reader.readLine(prompt)
-      line match {
-        case Some(cmd) => append(Exec(cmd, Some(Exec.newExecId), Some(CommandSource(name))))
-        case None      => append(Exec("exit", Some(Exec.newExecId), Some(CommandSource(name))))
+      try {
+        reader.readLine(prompt) match {
+          case Some(cmd) => append(Exec(cmd, Some(Exec.newExecId), Some(CommandSource(name))))
+          case None =>
+            println("") // Prevents server shutdown log lines from appearing on the prompt line
+            append(Exec("exit", Some(Exec.newExecId), Some(CommandSource(name))))
+        }
+      } catch {
+        case _: ClosedChannelException =>
       }
       askUserThread = None
     }